This invention relates to actuator systems of the type having an electric motor, typically connected to a gear train and an output shaft. Actuator systems are used to effect motion in a wide variety of applications. By way of example, actuators are used in automotive climate controls to set the various doors and louvers which will create the air flow desired by the user. These doors are used to blend heated, cooled or ambient air according to a selected temperature setting, and to direct the air to the selected vents.
Actuators are generally part of a control system that accepts instructions from a user and directs the movement of the actuators according to those instructions. The control system often needs to have information regarding the current position of an actuator. This can be provided by a potentiometer having a wiper movable with the output shaft of the actuator motor.
FIG. 1 shows a conventional five-wire actuator system. It has a microcomputer 10 with IC motor drivers 11 and an analog to digital converter 12. An actuator motor 13 is connected to the drivers 11 through pins 1 and 5. It will be understood that the motor has an output shaft connected to the device to be moved. The output shaft also carries the wiper 14 of a resistive-element potentiometer 15. The wiper is electrically connected to the A/D converter 12 through pin 3. A power supply 16 is connected to one side of the potentiometer through pin 2 while the other side is grounded through pin 4. A motor power supply 17 is connected to the two IC drivers 11.
In this system five wires are needed to connect the motor and potentiometer to the five pins. The output voltage on pin 3 is proportional to the rotational position of the actuator output shaft. Note that the potentiometer requires its own power supply 16, separate from the power supply 17 for the motor 13. The power supply 16 and its associated wiring add cost and complexity to the system. In some applications, such as the automotive climate control mentioned above, the costs can be about fifty cents per wire. The three-wire and four-wire systems of the present invention have been developed to minimize these costs.